Method of producing cathodes for hollow cathode lamps of spectroscopic analyzers



This invention relates to a new method of producing,

hollow cathodes to be used as light sources of spectroscopic analyzers depending on the atomic absorption method and other like apparatuses. I a

A spectroscopic analyzer depending on the atomic absorption method is to be understood herein as being of the following. description. Inthe use of thisanalyzer, the sample substance to be analyzed is transformed into a soluble substance such as, for example, a salt, and an aqueous solution thereoii is prepared andintroduced in an atomized form into the flame of agas burner so as to vaporize the sample. Then, when lightproje'cted from a light source consisting of a hollow cathode lamp passesthroughrthe said flame, this light is absorbed at a certain vwavelength 2 o a o is, the'requirement of being capable of obtaining line spectra of several kinds of elements from a single lamp.

:For this purpose, heretofore, in the analysis of several kinds of constituents, it has been necessary tochange the lamp in each case. Furthermore, in the case of metals of low melting points, such as Pb, Sn, and Zn, the use of a high current causes a rise in the lamp temperature to V i 500 to 600 degrees C. due-t the joule heat, whereby the elec'trode'made from a metal of low melting point melts,

For this reason, the current must be kept low, wherefore the luminous intensity is thereby reduced, and a satisfactory bright line cannot be obtained. 7

As one measure of eliminating the above-described disadvantages, the present inventors considered the use of an alloy for the cathode and made a fusible alloy "from zinc and copper. However, this alloy was found to have the 7 following disadvantageous features. -With this-alloy, two

kinds of line spectra are obtained. 'Moreover, when the alloying proportions are made to be 15 percent Zn and 85 percent Cu forthe sake of machinability, the zinc becomes a solid solution in the copper, the bright line forZn becoming remarkably weak, and a satisfactory linespectrum cannot be obtained. Furthermore, the intensity of the,

spectral line is'caused to drop in a short time by the determined by the sample substance. The quantity of this i absorption is detected by a spectroscopic apparatus'having such components as p f sms and detecting devices and is measured from the difference between the intensity of light received directly fromthe light source andthatiof the light 1 evaporation of the Zn in the surface layer, A fusible alloy ofSO percent Zn'and percent Cu was found to' be extremely brittle and diflicult to machine. As a result of research, a' method of producing a cathodehas been found by application of powder metallurgy which'fulfills which has passed through the sample. Fromthis measurement, the concentration of the element contained the sample being analyzed iscomputed.

By the above-describedmethod, precise analysisc'anbe performed rapidly withoutany influence due to other coexisting elements, even when the sample content is extremely small. In general, for this type olflightisource, one which has a highintensity' at a certain wavelength is considered to be necessary. Although an ordinary'white light source is anintense lightsource over a wide range of Wavelengths, since its lightintensity is fe ble .inthe narrow wavelength range necessary for analysis and is deficient in actual practice, the best line spectnlm to use is that of thesubstancetobe.measured;.for egampleif the substance to be measured is copper,"thebest,line spectrum to use is that of popper, i

The hollow cathode lamp has been dev'elopedin view of the above-presentedconsiderations. It i a obj c f he pres n invention ogprcvide a c d f r a holl w-c thod lampls i ying s ver l onditions, the principal conditions being as listed ,below.

(1) The hollow cathode should have anintense line spectrum at the time of dischargeand at thesame time, should, itself, exhibit a bright line of loW absorption.

(2) The cathode should have good electrical conductivity and thermal conductivity and-shouldhe free'ofloeal heating at the tirne of discharge. c v

(3) The cathode material should be such thatjit can be subjected to such fabrication processes as cuttingjinto the required configurationand drilling. I (4) The cathode should have a long working life. (5) In actual practice, the line spectra oftwo ormore elements should be obtainable from one lamp.

Heretofore, for this type of cathode, cathodes which do not melt when their temperatures rise during use up to 500 to 600 degrees C. for example, cathodes of Cu, Fe, Ni, Cr, Co, Au, Ag, -Rh, -Pd, Puma, and Ti, -have been used, the cathode in each case consisting of one kind of single, pure metal. However, although such a cathode satisfies the first four of theafore-listed requirements, it has been incapable of melting the fifth requirement, that -of the electrode, and the machining of product is greatly facilitated. Among elemental metals, such metal withshort lives as readily evaporating Zn and Cd or such i metals of low melting points as -Pb'and Sn can also be I .used, practically, as cathode metals as will be described I c .of the elemental metals.

all of the afore-listed requirements, and in which, moreover, even an alloy of low melting point metals can be used.

The essential characteristic of the method of producing a cathodes accordingto the present invention :isits procedure consisting of pulverizing at least two elemental metals selected from such metals as Cu,-Fe, Ni, Cr, Au, Ag, Pd, Bi, Sb, Pb, Sn, Zn, Pt, Ta, Ti, Mn, B, and Si, mixing and molding the said two metals in-pulvei'ized By the method of this invention, since the raw materials are in powder form, the molded article is in a mixture state of at least two kindsof materials. 'Whenthis article is heated, the said two materials mutually diifuse'in some cases, but by selectinga suitable heating temperature, it i is possible to increase the mechanical strength of the article while maintaining the mixture .state of the particles-i Accordingly, if two elemental metals have been used, two bright lines can be readily ;obtained.- Furthermore, by the method of this invention,

the article can be molded directly into the configuration hereinafter in an example,

Heretofore, an electrical contact pulverizing tungsten and 'addingthereto; such elements as silver and copper"has. beenlmanufacturedf Such a practice, as a production method, is similar to the method of the present invention. However, the aim in this known practice is to' utilize. the fact that tungsten, be- Y Q cause of its extremely high melting point, is a metal by 'which it is difficult to obtain a fusible metal material i and the fact that the high melting point of tungsten'pro vides resistance-against arcin and this; practice is fundamentally different in naturefrom the present in i ited States Patent Ofific $532123 material produced by V I In order to indicate still more fully thenature of the present invention, the following examples of typical procedure are set forth, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention. Throughout these examples, the term alloy is used to mean a combination of two or more metals in a mixture state, that is, the term includes a composite substance, a substance wherein diffusion between the metals has advanced because of heating, and, in some cases, a sintered substance wherein compounds have been formed.

Example 1 15 percent of Pb powder and 85 percent copper powder were mixed by means of mixing machines such as a ball mill and then compression molded. The molded powder mixture was thensintered for one hour at a temperature of from 600 to 650 degrees C. to produce an electrode to be used as a cathode.

Example 2 Three mixtures, respectively consisting of 30 percent Sn and 70 percent Cu, 40 percent Sn and 60 percent Cu, and 50 percent Sn and 50 percent Cu, all in powder form, were mixed in mixing machines such as a ball mill, and then each mixture was compression molded. Then each molded mixture was sintered at 200 to 350 degrees C., whereupon three cathodes were obtained.

Example 3 Three mixtures, respectively consisting of 30 percent Zn and 70 percent Cu, 40 percent Zn and 60 percent Cu, and 50 percent Zn and 50 percent Cu, all in powder form, were mixed in mixing machines such as a ball mill, and then each mixture was compression molded. Then each molded mixture was sintered at 300 degrees C., whereupon three cathodes were obtained.

Ineach of the sintered copper alloys produced according to the foregoing Examples 1, 2, and 3, the Cu assumed a sponge-like structure, and the interstices thereof were filled with the other metal, Pb, Zn, or Sn. For this reason, when the electrode temperature became 500 to 600 degrees C., and the Pb r Sn melted, or the Zn evaporated, the electrode did not change its shape. Accordingly, the intensities of both bright line spectra were amply high, and satisfactory bright line spectra for each of the metals Cu, Pb, Sn, and Zn were obtained.

The above-mentioned sponge-like structure is produced not only by Cu powder but also by powders of such metals as Fe, Ni, Co, and Cr.

Example 4 45 percent of Fe powder, 30 percent of Ni powder, and 25 percent of Cu powder were mixed by means of a ball mill and then compression molded. Next, the article thus compression molded was sintered for one hour at 900' degrees C. The sintered material was machined into an electrode. As a result of using this electrode, the intensities of the spectrum lines of the three elementswere substantially equal and were amply high. In all respects, a satisfactory electrode was obtained.

In all of the foregoing examplessintered alloys containing copper powder were produced. The inclusion of copper powder aifords the advantages of ease of molding and sintering, 'high electrical conductivity, relatively.

high melting points, and ease of fabrication such as machining. However, the present invention is not necessarily limited to the inclusion of copper powder, the inclusion of other substances producing equivalent results also being possible as indicated by the following Examples 5 and 6.

Example 5 50 percent of Ni powder and 50 percent of Mo powder were thoroughly mixed by means of a ball mill and then compression molded. The molded article was then sintered for one hour at 1,200 degrees C., in an atmos- 4 7 7 phere of hy drogen gas, and the sintered material was then machined into a cathode. As a result of using this electrode, the intensities of the spectrum lines of the Ni and M0 were substantially equal, and satisfactory results were obtained.

Example 6 27.5 percent of Co powder, 36.3 percent of Mo powder, and 36.2 percent of Cr powder were thoroughly mixed in a ball mill and then compression molded. The molded article was then sintered for one hour at 1,200 degrees C. in an atmosphere of hydrogen gas, and a cathode was made by machining the sintered material. As a result of using this electrode, the intensities of the spectrum lines of the three elements were substantially equal, and satisfactory results were obtained.

Since it is obvious that many changes and modifications can be made in the above described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to the details described herein except as set forth in the appended claims.

What we claim is:

1. A process of manufacturing a cathode for hollow cathode lamps in spectroscopic analyzers, which cornprises mixing the powders ofa high-melting elemental metal and a low-melting elemental metal, molding the mixture and sintering the same, thereby obtaining said high-melting metal in sponge form and the low-melting metal filling the interstices of said sponge; and further obtaining line spectra equalfto' the individual powdered metals used inkind 'andinumb er; and forming a cathode from the sintered mixture.

2. A process of manufacturing a cathode for hollow cathode lamps in spectroscopic analyzers, which comprises mixing powdered copper with the powder of a lowmelting elemental metal, molding the mixture and sintering the same, thereby obtaining said copper in sponge form and the low-melting metal filling the inerstices of said sponge; and further obtaining linespectra equal to the individual powdered metals used in kind and number; and forming a cathode from the sintered mixture.

3. A process of manufacturing a cathode for hollow cathode lamps in spectroscopic analyzers, which comprises mixing the powders of a high-melting elemental metal, selected from the group consisting of copper, iron, nickel, cobalt and chromium, with powders of a lowmelting elemental metal selected from the group consisting of lead, tin, and zinc, and sintering the mixture, thereby obtaining the high-melting metal in sponge form and the low-melting metal filling the interstices of said sponge; and further obtaining line spectra equal to the individual powdered metals used in kind and number; and forming a cathode from the sintered mixture.

4. A process of manufacturing a cathode for hollow cathode lamps in' spectroscopic analyzers, which comprises mixing the powdersof a highrmelting elemental metal selected from the group consisting of copper, iron, nickeL-cobalt and chromium, with powders of a lowmelting elemental metal selected from' the group con- ;sisting of lead, tin and zinc, in proportionsof high-melting to low-melting metal of 50:50 to :15 percent; and

sinteringthe mixture, thereby obtaining the high-melting metal in sponge, form and: the low-melting metal filling the interstices of said sponge; and further obtaining line spectra equal to the individual powdered metals used in kind and number; and forming a cathode from the sintered mixture.

References Cited in the file of this patent Great Britain AD. 1902 

1. A PROCESS OF MANUFACTURING A CATHODE FOR HOLLOW CATHODE LAMPS IN SPECTROSCOPIC ANALYZERS, WHICH COMPRISES MIXING THE POWDERS OF A HIGH-MELTING ELEMENTAL METAL AND A LOW-MELTING ELEMENTAL METAL, MOLDING THE MIXTURE AND SINTERING THE SAME, THEREBY OBTAINING SAID HIGH-MELTING METAL IN SPONGE FORM AND LOW-MELTING METAL FILLING THE INTERSTICES OF SAID SPONGE; AND FURTHER OBTAINING LINE SPECTRA EQUAL TO THE INDIVIDUAL POWDERED METALS USED IN KIND AND NUMBER; AND FORMING A CATHODE FROM THE SINTERED MIXTURE. 